by Claudia Puig, USA TODAY

by Claudia Puig, USA TODAY

PARK CITY, Utah - In The East, a clever thriller that blurs the line between right and wrong, working together is key among a group of radical eco-activists.

Three of the stars and director Zal Batmanglij say they enjoyed a collaborative, convivial spirit as they shot the film, which is premiering at the Sundance Film Festival.

"I don't think I've ever gotten that close to a cast and crew before," says Alexander Skarsgard. "Everyone was so passionate about it. Every single person behind the camera cared so much, too. It wasn't just a job."

Skarsgard plays Benji, the leader of an underground collective that employs guerrilla tactics to avenge corporate misdeeds. Brit Marling is Sarah, an intelligence agent who is sent to infiltrate the group but begins to feel some sympathy for those she was hired to investigate. Her confusion is complicated by a growing attraction to the charismatic Benji. Ellen Page plays Izzy, a fanatical group member who competes with Sarah for Benji's affections.

"What's weird is that spies and anarchists actually have a lot in common," says Marling. "They know how to pick locks, they know how to infiltrate. So Sarah, with all her espionage skills, is actually well-suited to be an anarchist, and she sort of finds that out along the way."

Adds Page: "I think the film creates this ethical murkiness, this gray zone that is very compelling. And I'm extremely interested to see it go out into the world and see how it provokes people and the conversation that it creates."

If Sundance is any indication, there should be plenty of discussion.

"At a screening today at 8 in the morning, we were walking out, and this woman grabs my arm,'' says Marling. "She's maybe in her mid-40s, and she's in tears and says, 'I work for a pharmaceutical company, and this movie just blew my mind. It's changing the way I think about everything, about my career, about what I do for a living, and I don't know what the answers are, and I don't know what it means about what I should do next, but I'm thinking about it.' It was really intense."

Batmanglij and Skarsgard encountered other shaken audience members.

"These CEOS came to where we were having dinner, and the gist of what they said was, 'If your movie can get us to have the conversation we just had at dinner, then imagine what else it can do,'" Batmanglij says.

Skarsgard says the process of developing his character with Marling, who co-wrote the script with Batmanglij, was "alive and organic. Something changes and becomes a little better the night before you shoot a scene. That's not always the case. You don't always work with filmmakers who are willing to invite you into that process."

To illustrate the spirit of teamwork on the set, Marling cites an example from the first day of shooting "where Ellen is basically naked on the ground with some flowers, and 12 people who she just met the day before are standing around staring down at her for an entire day. It was freezing cold, and it was an emotional, very intense day, and she just did it.''

Marling says her bravery "set the bar so high for the way in which we were all going to approach this work that the next day, when everybody had to get naked and bathe each other, nobody complained. Everybody just stripped down in the water and did it. The result was that there was this kind of intense intimacy with everybody and a real bravery in terms of approaching the work and the desire to go all the way there, even go way past the script."

Batmanglij and Marling say their shared love of thrillers generated the idea for the film.

"We'd been fascinated by the idea of activism and the idea of setting a thriller with a different backdrop," Batmanglij says. "I'm so tired of seeing corrupt CIA. Or now the Zero Dark Thirty badass CIA. There are other places that are thrilling. So we wanted to set a thriller in that space.''

A few summers ago, the pair spent a couple months traveling in a fashion similar to the movie's group, known as the East, to see if they could live for that long without spending money. They spent time with "freegans," an anti-consumer group who eat discarded food in their pursuit of a moneyless existence.

"We wanted to have some adventure, and we didn't have any money," says Marling. "We learned to hop trains, we learned to sleep on rooftops, we learned to claim the space that feels so private. We joined this anarchist collective."

Skarsgard was drawn to the film for its moral complexity.

"One of the reasons I fell in love with the script is because it was such a hot topic, but it wasn't propaganda," he says. "Even these eco-anarchists are not a monolithic group. Some of them are willing to go further than others. It's morally a very interesting question: How far are you willing to go? A person might be a terrorist to someone and a freedom fighter to someone else. It's a little more complicated than good guy vs. bad guy, which makes it interesting and real."

Now, after the two-month shoot in Shreveport, La., actors and filmmakers are especially eager to gauge audience reaction at the festival.

"It was a big moment to sit down and watch it with not only your friends, but also 1,300 strangers," Skarsgard says. "And it's kind of like, 'All right, here's our little baby, see what you think. I hope you like it.'"